Steering columns for vehicles tend to be formed by a steering shaft attached at one of its ends to the steering wheel and at the other end to the wheel axle, usually for the front wheels, of the vehicle by means of a universal joint. The axle can rotate inside a support structure fixed in the vehicle frame. The support structure can comprise an anchoring support and a tubular part, inside which the steering shaft rotates in bearings. Currently, it is very common for the steering wheel to be movable in depth, both for the purpose of being adjustable for the driver and for the purpose of damping the force of impacts in case of frontal collisions, for which purpose the tubular part comprises an outer welded bracket or tube and an inner tube which can move telescopically in the outer bracket or tube so that the steering wheel can be adjusted to different depths and so that the tubular part collapses in the case of a vehicle collision. It is also very common that the steering wheel can be adjusted in height, for which purpose the outer bracket or tube is assembled in the anchoring support by means of assembly systems which allow the angular lowering of the steering wheel.
In order to achieve a good slide between the inner tube and the outer bracket or tube, there have been provided outer tubes having a polygonal, usually orthogonal, outer cross-section provided on the external surface with longitudinal and planar external guiding faces which are guided in complementary facets provided inside the outer bracket or tube. In some steering columns it is foreseen that for supporting the bearings in which the inner rotating drive shaft from the steering wheel inside the inner tube rotates, the inner tube must have at least two end sectors having a circular cross-section in which the respective bearings are supported and delimiting between one another an intermediate sector having an outer polygonal cross-section with the mentioned external faces, one of the end sections must also conveniently have planar external areas that are a continuation of at least some of the planar faces of the intermediate sector in order to ensure a better slide, both in the adjustment of the depth of the steering wheel and in the case of collision.
Outer tubes having the mentioned end sector having a circular section and said planar external areas are known, obtained from a tube having a polygonal outer cross-section with an inner passage having a circular cross-section and a diameter less than that of the bearing which must be assembled in that end sector and increase the diameter of the inner passage in the corresponding end part of the inner tube by means of machining. These outer tubes must have enough wall thickness so as to be able to perform machining in said end part, so they are heavy, they require a lot of material mass truly unnecessary for their function, and imply a machining process, all of which increases the cost of the inner tube in terms of the material used and the manufacturing process.